Method of making a nickel hydroxide material

ABSTRACT

A process for making a positive battery electrode material using a secondary metal. The secondary metal is preferably treated using an non-electrolytic process and formed into an active, positive battery electrode material by a precipitation reaction.

REFERENCE TO RELATED APPLICATIONS

The present invention is a continuation in part of co-pending U.S.patent application 09/135,477, now U.S. Pat. No. 6,228,535 entitled“Nickel Hydroxide Positive Electrode Material Exhibiting ImprovedConductivity and Engineered Activation Energy” by Fierro et al., filedAug. 17, 1998; and 09/135,460, now U.S. Pat. No. 6,177,213 entitled“Composite Positive Electrode Material and Method for Making Same” byFetcenko et al., filed Aug. 17, 1998; and 09/153,692, now U.S. Pat. No.6,086,843 entitled “Structurally Modified Nickel Hydroxide Material andMethod For Making Same” by Ovshinsky et al., filed Sep. 15, 1998, thedisclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention pertains to a method for making high densitynickel hydroxide for alkali rechargeable batteries. More particularly,the present invention pertains to a method for making nickel hydroxidefor a battery electrode from a secondary low cost nickel source.

II. Description of the Background Art

The demand for batteries has grown dramatically over the past decade andcontinues to grow at a phenomenal rate. Rechargeable batteries with highenergy density and high capacity are particularly desirable. Two typesof batteries that are widely used are the Ni—Cd (nickel cadmium) typeand the more desirable Ni—MH (nickel metal hydride) type. Thesebatteries have a positive and negative electrode. In both types ofbatteries the positive electrodes are made primarily of nickel hydroxideactive material.

Ni—MH cells utilize a negative electrode that is capable of thereversible electrochemical storage of hydrogen. Ni—MH cells usuallyemploy a positive electrode of nickel hydroxide material. The negativeand positive electrodes are spaced apart in an alkaline electrolyte.Upon application of an electrical potential across a Ni—MH cell, theNi—MH material of the negative electrode is charged by theelectrochemical absorption of hydrogen and the electrochemical dischargeof a hydroxyl ion, as shown in equation 1.

M+H₂O+e⁻⇄M−H+OH⁻  (1):

The negative electrode reactions are reversible. Upon discharge, thestored hydrogen is released to form a water molecule and release anelectron.

The reactions that take place at the nickel hydroxide positive electrodeof a Ni—MH cell are shown in equation 2.

Ni(OH)₂+OH⁻⇄NiOOH+H₂O+e⁻  (2):

The use of nickel hydroxide, Ni(OH)₂, as a positive electrode materialfor batteries is generally known. See for example, U.S. Pat. No.5,523,182, issued Jun. 4, 1996 to Ovshinsky et al., entitled “EnhancedNickel Hydroxide Positive Electrode Materials For Alkaline RechargeableElectrochemical Cells”, the disclosure which is herein incorporated byreference.

Several forms of positive electrodes exist at the present and includesintered, foamed, and pasted electrode types. Processes for makingpositive electrodes are generally known in the art, see for example U.S.Pat. No. 5,344,728 issued to Ovshinsky et al., the disclosure of whichis herein incorporated by reference, where capacity in excess of 560mAh/cc was reported. The particular process used can have a significantimpact on an electrode's performance. For example, conventional sinteredelectrodes normally have an energy density of around 480-500 mAh/cc.Sintered positive electrodes are constructed by applying nickel powderslurry to a nickel-plated, steel base followed by sintering at hightemperature. This process causes the individual particles of nickel toweld at their points of contact, resulting in a porous material that isapproximately 80% open volume and 20% solid metal. This sinteredmaterial is then impregnated with active material by soaking it in anacidic solution of nickel nitrate, followed by the conversion to nickelhydroxide by reaction with an alkali metal hydroxide. Afterimpregnation, the material is subjected to electrochemical formation.

To achieve significantly higher loading, the current trend has been awayfrom sintered positive electrodes and toward pasted electrodes. Pastedelectrodes consist of nickel hydroxide particles in contact with aconductive network or substrate, most commonly foam nickel. Severalvariants of these electrodes exist and include plastic-bonded nickelelectrodes, which utilize graphite as a microconductor, and pastednickel fiber electrodes, which utilize spherical nickel hydroxideparticles loaded onto a high porosity, conductive nickel fiber or nickelfoam support.

The production of low cost, high capacity nickel hydroxide is criticalto the future commercialization of Ni—MH batteries. As with electrodeformation, the properties of nickel hydroxide also differ widelydepending upon the production method used. Generally, nickel hydroxideis produced using a precipitation method in which a nickel salt and ahydroxide salt are mixed together followed by the precipitation ofnickel hydroxide. Active, nickel hydroxide material preferably has highcapacity and long cycle life, see U.S. Pat. No. 5,348,822 to Ovshinskyet al., the disclosure of which is herein incorporated by reference.

It has been discovered that nickel hydroxide suitable for use in abattery electrode should have an apparent density of 1.4-1.7 g/cm³, atap density of about 1.8-2.3 g/cm³, and a size range of about 5-50 μ.Active, nickel hydroxide particles are preferably spherical in shapewith a high packing density and a narrow size distribution Preferably,average particle size should be about 10 μm and tap density should beabout 2.2 g/cc. Paste made with this kind of nickel hydroxide has goodfluidity and uniformity, and thus it is possible to fabricate highcapacity, uniformly loaded electrodes. The use of this kind of nickelhydroxide also improves the utilization of the active material anddischarge capacity of the electrode. If the process is not carefullycontrolled, the precipitate will have an irregular shape and/or low tapdensity. For example, if the rate of reaction is too fast, theprecipitate formed may be too fine and the density too low. A finepowder with low density requires longer filtering or washing times andincreases the adsorption of water on the surface. Further, if theprecipitated particles have too wide a size distribution (ranging from 1to hundreds of microns), the nickel hydroxide may require pulverizationto render it useful. Electrodes formed with low-density nickel hydroxidewill lack high capacity and high energy density. For these reasons andothers, an active powder having an irregular shape and/or low density isless than desirable for use as a high capacity battery electrodematerial.

In order to produce high density, substantially spherical nickelhydroxide, particles are gradually grown under carefully controlledprocess conditions. A nickel salt provided in solution is combined withan ammonium ion. The nickel salt forms complex ions with ammonia towhich caustic is added. Nickel hydroxide is then gradually precipitatedby decomposition of the nickel ammonium complex. The reaction rate isdifficult to control, so methods have been introduced to separatecritical steps in the production process to compensate for saiddifficulties. For example, U.S. Pat. No. 5,498,403, entitled “Method forPreparing High Density Nickel Hydroxide Used for Alkali RechargeableBatteries”, issued to Shin on Mar. 12, 1996, the disclosure of which isherein incorporated by reference, discloses a method of preparing nickelhydroxide from a nickel sulfate solution using a separate or isolatedamine reactor. Nickel sulfate is mixed with ammonium hydroxide in theisolated amine reactor to form a nickel ammonium complex. The nickelammonium complex is removed from the reactor and sent to a second mixingvessel or reactor where it is combined with a solution of sodiumhydroxide to obtain nickel hydroxide. Such a method relies heavily on araw material source of very high purity or what is termed throughout theensuing'specification as primary nickel.

Thus, particular notice should be taken in the fact that all of presentday processes for making positive electrode materials, such as thosedescribed above, have utilized expensive, high grade, and highly pureprimary nickel for the production of nickel salt starter solutions. Asmodern process technology and automation have reduced the cost of laborin the production of battery electrode materials, the cost of primarynickel and its associated salts have become a significant factor indetermining the cost of active electrode materials, battery electrodes,and the batteries the electrodes are placed within, making up as much as60% of the direct manufacturing cost of the final nickel hydroxide.

Primary nickel used for the production of active materials is typicallyderived from the ores of nickel sulfide and nickel oxide and purified byelectro-processes. Nickel sulfide ores are refined by flotation androasting to nickel oxide. Nickel oxide ores are typically refined byhydrometallurgical refining, such as leaching with ammonia. Refinednickel ore is usually cast into nickel anodes for distribution asprimary nickel. The highly pure, primary nickel may then be dissolvedinto solution, such as a sulfate solution, and sold as highly pureaqueous nickel sulfate, with a frequent end use also being nickelelectroplating and electroless nickel plating.

The average amount of nickel estimated to be present in the earth'scrust is only about 0.0084 wt %, as reported on page 14-14 of theHandbook of Chemistry and Physics, 78th Edition, 1997-1998. Becausenickel is used for many things, including the production of stainlesssteel, the demand for nickel is very high, making it a relativelyexpensive metal. Although primary nickel is a commodity product, it issubject to wild market swings in price. For example, during the periodof Jun. 1, 1999 through June 1, 2000, nickel prices have seen dramaticvolatility having a low of 2.16 $/lb and a high of 4.77 $/lb as reportedon the London Metal Exchange. As a means of off-setting or hedgingagainst the increasing cost of nickel, a number of large producers ofnickel hydroxide have gone so far as to purchase ownership interests innickel mines. Smaller manufactures of nickel hydroxide, unable to offsetrising nickel prices, have been left at a competitive disadvantage.

Thus, present day methods of producing nickel hydroxide from highly purenickel lack a material independent source of nickel that is not drivenby the market costs of primary nickel.

One particular source of nickel not presently utilized for theproduction of nickel hydroxide for battery electrodes is that ofsecondary nickel or nickel by-product. Secondary nickel is that nickelwhich is derived from either process or waste streams unrelated toprimary nickel or the production of high purity nickel, or is nickelfrom spent or virgin solutions used in electroplating or electrolessplating of nickel. One way to characterize secondary nickel is by itshistory of use. Although present methods may exist for refining nickel,see for example U.S. Pat. No. 5,861,131, the disclosure of which isherein incorporated by reference, such methods do not provide asecondary nickel source of suitable quality for the production of nickelhydroxide materials used in battery electrode materials. Additionally,the background art fails to teach or suggest the use of any secondarynickel or nickel by-products for use in active battery electrodematerials, especially nickel hydroxide production. While these secondarynickel sources cannot be classified entirely as waste, the cost of usingsecondary nickel dramatically reduces overall cost of active materials.

Thus, there exists a long felt and presently unfulfilled need for analternative to primary nickel for the production of battery electrodesand electrode materials.

SUMMARY OF THE INVENTION

The subject invention addresses the above stated problems and others by,among other things, providing a method for making nickel hydroxide usinga novel starting material. Nickel electroplating and electroless platingsolutions, including both virgin and spent solutions and various typesof waste streams having metal ions are generally known but have notheretofore been used to produce active, battery electrode materials.Thus, the present invention provides a new use for a secondary metal ormetal waste stream, by using the metal as a starter material for theproduction of an active, positive electrode material.

The battery electrode material is preferably a substantially spherical,high density nickel hydroxide material or nickel oxyhydroxide material,which may comprise one or more modifiers or modifier elements. Preferredmodifier elements include those selected from the group consisting ofAl, Ba, Bi, Ca, Co, Cr, Cu, F, Fe, In, K, La, Li, Mg, Mn, Na, Ru, Sb,Sn, Sr, Ti, and Zn, etc. In particular, modifiers of Co, Zn, Ca, Mg, Cu,Al and Li are more preferred.

Generally, the invention provides a method for making nickel hydroxidebattery electrode materials from secondary nickel or a secondary nickelsource where nickel is a by product.

The method includes the steps of: providing secondary nickel as a sourceof nickel; formulating the secondary nickel into a solution; adding aprecipitating agent to the solution in an amount effective toprecipitate a nickel salt; separating the nickel salt from the solution;dissolving the separated nickel salt into a nickel salt solution;evaporating a portion of the nickel salt solution to precipitate anickel salt precipitate; and converting the nickel salt precipitate intoan active positive electrode material.

A second aspect of the invention recognizes that to utilize thesecondary nickel source, the precipitation process is crucial to theultimate suitability of the. nickel hydroxide end product. Thus, asingle precipitation reaction, instead of the common two reactor systemwith a preamine initial reaction, allows the use of a secondary nickelsource.

A third aspect of the invention recognizes that the utilization of asecondary nickel source need not be an all or nothing proposition, andthat particular end formulas of the nickel hydroxide may have more orless tolerance to the secondary nickel source. The method therebyrecognizes that the “as is” secondary nickel source may be substitutedat least in part due to the presence of impurities and concentrationdifficulties. A novel approach of blending solutions using primary andsecondary nickel is disclosed.

A fourth aspect of the invention recognizes that the battery end use maydictate certain performance properties, such as paste loading andcapacity. In this case, a novel approach of blending nickel hydroxidemade from primary nickel together with nickel hydroxide made fromsecondary nickel is disclosed.

Still, another aspect of the invention is to recycle “out ofspecification nickel hydroxide” back into nickel sulfate solutionsuitable for making new nickel hydroxide. The “out of specificationnickel hydroxide” may be reactor startup scrap, transition materialformed between chemical formula changes, or material resulting fromproduction issues such as power outages, equipment failure, etc.

Nickel hydroxide material produced in accordance with the present methodprovides particles having a shape, a particle size, a tap density, and acrystallinity suitable for use as an-active positive electrode material.For a more complete understanding of the present invention, reference ismade to the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a system for preparing nickel hydroxide inaccordance with a preferred aspect of the present invention;

FIG. 2 is a magnified view of nickel hydroxide prepared by the method ofthe present invention with secondary nickel;

FIG. 3 is a magnified view of nickel hydroxide material prepared by themethod of the present invention using a 50% raw material blend; and

FIG. 4 is a process flow diagram of a method for preparing nickelhydroxide in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a novel precipitation process used to make nickelhydroxide from either primary or secondary nickel sources without apreamine reactor, the process of which is discussed in detail below. Asingle reactor system is preferred for practicing the present inventionas the single reactor system provides improved process control, avoidspremature precipitation, and permits greater system tolerance forunknown dissolved materials.

Now referring to FIG. 4, generally depicted therein at 100 is a processflow diagram of a method for making a nickel hydroxide active materialfrom an initial, secondary metal source having unknown dissolvedmaterials in accordance with the present invention. The secondary metalsource is preferably a secondary nickel source having at least onecontaminate that adversely effects the utilization of the metal sourcefor electroplating and electroless nickel plating. The secondary nickelsource may also be of unsuitable quality for use as a battery electrodematerial if used directly in a nickel hydroxide production process.

The secondary nickel source surprisingly substitutes as a raw materialsource for high purity nickel, thus such nickel is termed secondarynickel. Secondary nickel is defined as any nickel metal, nickel metalalloy or other nickel containing material where nickel is provided as aby-product or as a waste metal from a metal process stream or a metalwaste steam. Primary nickel, on the other hand, is high. purity nickeltypically obtained from nickel ore and. Primary nickel is oftenelectrolytically refined or cast into a single crystal anode fordistribution, e.g. is refined by an electro-process as opposed to anelectroless processes. Primary nickel is high purity nickel, such asreagent grade nickel having metal impurities of less than 0.05% byweight. Secondary nickel, on the other hand, is preferably provided asresidual, used, or waste nickel from a metal process stream, such as ametal plating bath, plating waste stream, metal electrorefiningoperation, electroplating operation, nickel plating solution, nickelelectroplating operation, electroless nickel plating operation, copperrefining operation, copper plating operation or any combination thereof.The secondary nickel may be a spent or virgin solution. Thus. one mannerof characterizing secondary nickel is from its history of use as beinginitially prepared for a process other than making nickel hydroxide oras being used material from a commercial process.

The secondary nickel source may supply nickel in any suitable form. Forexample, the secondary nickel source may supply nickel in either a solidor solution form. The nickel of the secondary nickel source ispreferably supplied as a nickel sulfate solid or a nickel sulfatesolution. The nickel may also be provided as nickel nitride, nickelchloride, nickel acetate, nickel carbonate, etc. If the nickel isprovided as a nickel salt in the form of a solid, the nickel salt ispreferably converted to a sulfate solution. Changing the nickel salt to.a nickel sulfate solution may be accomplished by any suitable method,for example, ammonium extraction, precipitation and redissolution withconcentrated sulfuric acid. A nickel sulfate starter solution provides areadily usable form of nickel for the production of active, nickelhydroxide material.

The initial, secondary nickel source may comprise a wide range ofcontaminants including both organic materials and inorganic materials.Undesirable contaminates, unlike modifiers, are contaminants that mayinterfere with the proper functioning or construction of the positiveelectrode due to elemental properties or an overly high concentration.The secondary nickel or nickel source may have at least one contaminantmetal selected from the group of elements consisting of Fe, Cu, Mn, Pb,Ca, Mg, Na. These contaminants may enter the nickel solution from anumber of sources, such as during normal or irregular productionprocesses, like during an electroplating operation for example.Undesirable contaminates also include elements or compounds that couldinterfere with the nickel hydroxide formation process itself, such asproper precipitation of nickel hydroxide. For instance, a highconcentration of contaminants can result in low energy density, lowcapacity, low tap densities, low surface areas, poor particle shape orpoor crystallinity, etc. In any respect, if the initial secondary nickelsource has contaminants that are higher than those reported as traceelements in high purity nickel, such as greater than 0.05 wt %, and morepreferably greater than 0.4 wt % or higher, such as: greater than 4 wt%, greater than 6 wt %, greater than 8 wt %, greater than 10 wt % orgreater than 12 wt %. As such, secondary nickel sources having such highcontaminate concentrations have not heretofore been used as a nickelhydroxide starter material.

It has been particularly found that when sodium is present in theinitial secondary nickel source at a concentration of greater than 9%total dissolved metals, the secondary nickel or nickel source may effectthe production quality of nickel hydroxide powder. For example, it hasbeen found that when sodium is present in the initial secondary nickelsulfate solution at in amount greater than 4 g/l, nickel hydroxideproduced from the secondary nickel source has poor crystallinity and lowtap density.

The secondary nickel source may additionally include minor amounts ofelements that may be beneficial to or neutral to the final activeproduct. Beneficial elements include various modifier elements. Theseelements may be present in low amounts of less than 9 wt % and includeCo, Zn, Mg, Ca, Mn, Cu, etc., as discussed in detail in U.S. patentapplication Ser. No. 5,348,822 and co-pending U.S. patent applicationsSer. Nos. 09/135,477 and 09/135,460.

For example, commercial nickel sulfate is sold with a high purity level,such as less than 0.05% dissolved metals. The following is an ICPanalysis in g/l of primary nickel in the form of a nickel sulfatesolution.

Ni: 151.1

Co: 0.0

Cd: 0.0

Zn: 0.0

Fe: 0.0

Cu: 0.0

Mn: 0.0

Pb: 0.0

Ca: 0.0

Mg: 0.0

Na: 0.03

Secondary nickel is not very pure, in fact secondary nickel contains amultitude of contaminants. The following is an ICP analysis in g/l of asecondary nickel in the form of a spent nickel sulfate solution from anickel plating operation.

Ni: 136.7

Co: 0.0

Cd: 0.0

Zn: 0.0

Fe: 0.36

Cu: 0.12

Mn: 0.08

Pb: 0.0

Ca: 0.85

Mg: 0.22

Na: 16

Regardless of what form the initial secondary nickel is provided as,i.e. whether the secondary nickel is a solid or in a solution, thesecondary nickel is eventually converted to or provided as a nickel saltsolution. The nickel salt solution preferably has a concentration of atleast 100 g/l of nickel to the maximum solubility level of nickel. Thenickel salt solution is preferably a nickel sulfate solution. It hasbeen found that low levels of nickel can form excellent nickel hydroxidematerial where nickel is present at levels of only 100 g/l to 140 g/l byusing the single reactor system of the present invention.

The nickel salt solution is preferably taken through at least oneprecipitation reaction to remove undesirable contaminants and provide anickel salt precipitate. The precipitation reaction may be accomplishedby any suitable precipitating agent. Preferably the precipitating agentis a carbonate salt solution. The carbonate is added in an amounteffective to precipitate nickel carbonate. As such, the carbonate ispreferably added in excess to the nickel salt solution. The carbonatemay be any type of carbonate capable of precipitating a nickel carbonatesolid, such as sodium carbonate, potassium carbonate, sodiumbicarbonate, potassium bicarbonate, combinations of the above, or thelike. The carbonate is preferably a sodium carbonate solution. With anexcess amount of sodium carbonate added to the nickel salt solution,nickel carbonate readily precipitates out leaving behind variousorganics, inorganics, nitrogen containing compounds, and surfactants,including large amounts of copper and sodium. It has been found by thepresent inventors, that despite the added costs of extra processing,savings in raw material costs more than offset the extra processingsteps. Thus, the present invention provides a method of making nickelhydroxide with a secondary metal using a non-electrolytic means orprocess for reducing the contamination of the secondary nickel in anamount sufficient for use in as active battery material.

The nickel salt precipitate is separated from the carbonate solution byfiltering or decanting and rinsed to remove additional contaminates.Filtering includes any of the known filtering methods, such as gravityfiltration, vacuum filtering, etc. Rinsing includes washing theprecipitate with water and/or other solvents, such as ethanol, toluene,acetone, etc. Separating the nickel salt precipitate from the initialsolution leaves behind various contaminants that readily dissolve inwater and/or the-other solvents.

The nickel salt precipitate is next redissolved in solution andre-precipitated as a nickel sulfate starter salt of suitable quality foruse in making an active positive electrode material. Preferably, thenickel salt precipitate is dissolved in sulfuric acid to form a nickelsulfate solution and then precipitated out with a condensationprecipitation step. The sulfuric acid is preferably concentratedsulfuric acid having a concentration range of 50% to 99%. A condensationprecipitation step provides superior nickel sulfate in comparison tonickel sulfate without a condensation precipitation step. For example,the nickel carbonate precipitate formed above may be dissolved insulfuric acid to form a nickel sulfate solution. The sulfuricacid/nickel sulfate solution is then diluted with water. Water isevaporated from the nickel sulfate solution to precipitate a nickelsulfate solid. The nickel sulfate solid is separated from the sulfatesolution by any suitable separation process, such as filtration,decantation, etc. The nickel sulfate solid may then be redissolved inwater to form aqueous nickel sulfate suitable for use as a nickelhydroxide starter solution.

The aqueous nickel sulfate starter solution is used to form high qualitynickel hydroxide material. As shown in FIGS. 1 and 4, nickel hydroxidematerial is preferably prepared by simultaneously combining the nickelsulfate starter solution made from a secondary nickel source, sodiumhydroxide and ammonium hydroxide in a single reaction vessel to formnickel hydroxide particles. The combined solution is preferablycontinuously and rapidly stirred or agitated. Nickel hydroxideparticulates are grown at a temperature and a pH that readilyprecipitates nickel hydroxide upon formation. The nickel hydroxidematerial produced in accordance with the present invention has highdensity, uniform, spherical particles with a crystallite size of lessthan 120 angstroms. This is in sharp contrast to materials of the priorart where the particles typically have crystallite sizes greater than120 angstroms. More specifically, the crystallite size of the particlesof the nickel hydroxide material are produced in the range from 50-150angstroms, more preferably 60-103 angstroms and most preferably 70-100angstroms. These materials provide superior capacity and are thereforedesignated high quality nickel hydroxide material.

A second aspect of the invention recognizes that to utilize thesecondary nickel source, the precipitation process itself is crucial tothe ultimate formation of high quality nickel hydroxide end product. Asingle precipitation reactor, instead of the common two reactor systemwith a preamine initial reactor, allows the use of a modified secondarynickel source. The inventors believe that a preamine reactor or preamineprocess is especially undesirable in accommodating a secondary nickelsource having impurities greater than those found in commercial, highpurity nickel sulfate.

Now in more detail and as briefly described above, the present inventionprovides a process for making active positive electrode materials usinga secondary nickel source, the process of which is shown in FIG. 1. Theprocess comprises combining MeNO₃, MeSO₄(3), NH₄OH(5) and NaOH(7) in asingle reactor (10), maintaining the reactor at a constant temperatureof 20-100° C. (more preferably 40-80° C. and most preferably 50-70° C.),agitating (9) the combination at a rate of 400-1000 rpm (more preferably500-900 rpm and most preferably 700-850 rpm), controlling the pH (11) ofthe agitating combination at a value between 9-13 (more preferably at10-12 and most preferably at 10.5-12.0) and controlling both the liquidphase and vapor phase ammonia concentration. The Me or metalcombinations set forth above include Ni, various metal modifier(s) thatwill be incorporated into the final modified nickel hydroxide materials,and contaminants. Additional modifiers may be selected from the groupconsisting of Al, Bi, Co, Cr, Cu, Fe, In, La (and other rare earthmetals), Mg, Mn, Ru, Sb, Sn, Ti, Zn, Ba, Si and Sr.

The MeSO₄ solution is formulated by mixing 3-30 wt %, more preferably5-25% and most preferably 7-12% nickel as nickel sulfate with othersulfate solutions containing the desired modifier(s). Overall, the metalsulfate solution added to the reactor is 0.05-3 M, more preferably 0.5-3M and most preferably 1-3 M. The NH₄OH solution added to the reactor is1-15 M, more preferably 5-15 M and most preferably 10-15 M solution. TheNaOH solution added to the reactor is 5-50 wt %, more preferably 8-40 wt% and most preferably a 15-30 wt %. Deionized water is preferably usedthroughout for all necessary dissolutions and dilutions.

As stated above, the pH of the mixture in the reactor must becontrolled. The control of the pH can be accomplished by any appropriatemethod, preferably through the addition of a base as needed. Theaddition of a base such as KOH or NaOH is preferred. Most preferably,20-60 wt % KOH or NaOH is used. The temperature of the mixture in thereactor should be maintained at the temperatures described above. Inorder to assure optimum contact between the components of the mixtureintroduced into the reactor, constant mixing or agitation should beprovided. Mixing may be provided by any suitable method, such asstirring, agitating, vortexing or ultrasonic, but must attain theagitation rates as set forth herein above.

In order to efficiently incorporate calcium into the bulk of themodified nickel hydroxide material of the present invention, it ispreferable that the calcium is not part of the metal sulfate solution(MeSO₄), rather, calcium should be formulated using a separate solutionand introduced using a separate feed stream. Preferably, the feed streamis CaCl₂ or other solublizing solution, such as calcium nitrate, calciumacetate, etc. where Ca may be introduced independently to the reactor. Aseparate solution may also be used for other insoluble materials thatare desired to be provided in the bulk active material. The Ca saltsolution introduced into the reactor is 0.005-20 wt %, more preferably a0.005-2.0 wt % and most preferably 0.005-1.0 wt %. Thus, in a preferredembodiment of the preset invention, the method provides a novelcontinuous precipitation process that is capable of producing a nitratefree active positive electrode material.

The addition of each of the components and the removal of the resultantslurry (containing precipitated nickel hydroxide material) is carefullycontrolled at complimentary rates so that the slurry contains a maximumamount of precipitate and a minimum amount of un-reacted components. Theabove described operating conditions for a continuous process haveprovided a remarkably high yield of 99.98%. The process is novel inseveral respects. First, it is completely new to apply a continuouslystirred tank reactor (CSTR) concept to the manufacture of nickelhydroxide. Prior art references (see Hyundai Motor Company Pat. No.5,498,403) indicate the necessity of employing two reactors, in series,involving the formation of a preamine complex. The two reactor approachhas been considered vital in order to achieve high density, sphericalnickel hydroxide particles. However, the inventors believe two reactorsin fact produce tremendous difficulties in balancing two vastlydifferent reaction rates, that being the preamine complexing and theactual nickel hydroxide precipitation which possess a number ofdisadvantages. Disadvantages of a two reactor approach include:

premature precipitation in the first reactor resulting in poor tapdensity and uncontrolled particle size.

poor yield because very high excess ammonia must be used in the firstreactor.

high effluent usage because of the need for dilute sulfate solution.

complexity from an automatic control standpoint in balancing tworeaction rates.

Premature equipment failure from corrosion in the second reactor due tothe high pH (>12) necessary to break the nickel ammonia complex.

The prior art, two reactor approach was also considered vital to ensurethe formation of a nickel ammonium complex prior to precipitation, toslow the precipitation reaction and allow high density particles toform. The objective of high powder density cannot be overstated for usein batteries, as active material loading is crucial to the energydensity of the overall positive electrode and the overall batterysystem. All known attempts to precipitate high density spherical nickelhydroxide without careful formation of the nickel ammonium complex failto achieve commercially viable high density material which hasinevitably led to a worldwide use of the two reactor manufacturingprocess.

The present inventors have also found that a CSTR approach vastlysimplifies processing. The inventors realized that the nickel ammoniumcomplex can be formed and destroyed simultaneously, that a short-lifenickel ammonium complex is not a problem as normally thought by others.Therefore, under the reactant concentrations described previously, andthe reactor conditions of temperature, mixing, pH and constituentconcentrations, formation of the nickel ammonia complex and subsequentimmediate precipitation to nickel hydroxide can occur simultaneously.The inventors have further recognized that the single reactor CSTRprocess can be used with a number of advantages, including:

the use of highly concentrated reactant solutions, effectively reducingthe amount of effluent streams.

the use of lower pH, thereby extending equipment and process controllife and reliability.

eliminating the need to “balance” two reactors, thus enhancingsimplicity in processing.

Once the slurry is drawn off from the reactor, it is filtered toseparate the precipitate from the liquid. The liquid is then recycledand the precipitate processed to produce the modified nickel hydroxideof the present invention.

It is thus possible to produce nickel hydroxide materials having threemodifiers, four modifiers, or more without premature precipitation andprocess failure. These modifier elements are preferably selected fromthe group consisting of: Al, Bi, Ca, Co, Cr, Cu, Fe, In, La, Mg, Mn, Ru,Sb, Sn, Ti, Y, and Zn. Preferred multi-element modifiers are used toform nickel hydroxide materials having a base formula selected from thefollowing:

(NiCo)(OH)₂

(NiCoZn)(OH)₂

(NiCoZnMgCa)(OH)₂

(NiCoZnMnMgCa)(OH)₂

(NiCoZnMgCaCuMn)(OH)₂

These modifies may be supplied with the initial, secondary nickel oradded at a separate stage in the process. Compositional modifiers may beadded in an amount sufficient to improve various characteristics of thepositive electrode, many of which are known to those skilled in the artof making said electrodes. As such, a secondary nickel or nickel sourcehaving minor amounts of the above modifiers may be particularly usefulin preparing nickel hydroxide materials for a battery electrode.Examples of nickel hydroxide materials having varying compositions andapplicable to the present invention include those described above, inthe background and others, including U.S. Pat. Nos. 5,523,182; 5,48,822;5,344,728; and 6,019,955, the disclosures of which are hereinincorporated by reference.

For other examples of nickel hydroxide materials particularly applicableto the present invention, see also commonly assigned, co-pending U.S.patent application Ser. No. 09/135,460, entitled “Composite PositiveElectrode Material and Method for Making Same” filed Aug. 17, 1998.Disclosed therein is a composite positive electrode material for use inelectrochemical cells. The composite material is formed with high puritynickel to produce nickel hydroxide powder particles having a conductivematerial at least partially embedded within the particles. The compositematerial may be formed by combining a metal ion solution, a causticsolution, and the conductive metallic material whereby a compositeprecipitate is formed. The combining step may comprise mixing the metalIon solution and the conductive material to form a suspension and addingcaustic to precipitate a composite, positive electrode material.

EXAMPLE 1.

NAOH from tank 12, MeSO₄ (consisting of secondary NiSO₄, CoSO₄, MgSO₄and ZnSO₄ from tank 14, NH₄OH from tank 16, and Ca(NO₃)₂ from tank 18were introduced into the reactor 10. As the ingredients were introduced,they were constantly stirred, as by propeller 20, at about 850 rpm andthe contents of the reactor were maintained at about 50° C. The pH ofthe mixture was maintained at about 12. The resulting precipitate ofmodified nickel hydroxide material is depicted in FIG. 2 and had thefollowing target metal composition:

Ni₉₁Co_(4.5)Zn_(4.5)  (1)

This process was repeated with modified quantities of precursorconstituents to yield modified nickel hydroxide having the followingtarget metal compositions in atomic %:

Ni₉₁Co₇Zn_(0.5)Mg_(0.5)Ca₁  (2)

Ni_(93.5)Co₅Zn_(0.5)Mg_(0.5)Ca_(0.5)  (3)

Ni₉₁Co₃Zn₁Mg₁Ca₂Cu₂  (4)

Ni₉₅Co₃Zn_(0.5)Mg_(0.5)Ca₁  (5)

Ni_(90.5)Co₃Zn₁Mg₁Ca_(2.0)Cu_(1.5)Al_(1.0)  (6)

Ni₈₆Co₇Zn₆Mg_(0.5)Ca_(0.5)  (7)

Ni₉₃Co₅Zn_(0.5)Mg_(0.5)Ca₁  (8)

In the processing method of the instant invention, great care must betaken with certain unexpected processing parameters. For instance, theliquid saturation of ammonia versus its vapor or head space saturationin the reactor is critical. The present inventors have found the ammoniaconcentration in the reactor significantly influences the finalproperties of the resultant powder with respect to crystallinity and tapdensity. Since ammonium hydroxide is continuously metered into thereactor, but is present in excess, part of the ammonia must be removedvia the reactor head space. The inventors have found that care must beexercised to avoid a “crust” forming on the top of the liquid; that isto avoid the liquid surface area in the reactor that is exposed to airfrom inadvertently charring. The inventors also control the incoming andexiting air stream in terms of air flow rate and humidity. For a 100kg/day reaction vessel, the inventors have determined that an air flowof about 50 or greater ft³/minute is adequate, with a relative humiditybelow about 65%. Properly managed, the materials of the presentinvention having the proper density and degree of crystallinity areconsistently obtainable in volume production. If, on the other hand,process parameters, such as head space saturation or concentration ofammonia are ignored, it is more likely than not that poor quality nickelhydroxide material will be produced.

Nickel hydroxide materials having the target composition of(Ni₉₁CO_(4.4)Zn_(4.5))(OH)₂ were produced in accordance with the presentinvention using a single reactor system described above with one sampleusing primary nickel sulfate and the other using secondary nickelsulfate. The active materials were formed into sealed c-cells in amanner well known in the art and tested for capacity at c/5 dischargerates at room temperature. The results are listed below in Table 1.

TABLE 1 CAPACITY COMPARISION Primary Nickel Secondary Nickel Rate c/5c/5 CAP (0.9 V)/Ah 5.02 5.06 % C/5 CAP 100 100 CAP (1.0 V)/Ah 4.96 4.90% C/5 CAP 99 98 MIDPOINT/V 1.23 1.19

The results in Table I show that nickel hydroxide material made withsecondary nickel, does not suffer significant reduced capacity at a c/5discharge rate.

The present invention may optionally include one or more blending steps.Blending may be used to improve the composition of the initial nickelsulfate solution, an intermediate solution or the final nickel hydroxideproduct. The optional blending step may include blending the initialsecondary nickel source as in a raw material blending step, blendingintermediate solutions, and/or blending the final, nickel hydroxideproduct. As the present invention encompasses a wide range of secondarynickel sources, blending provides a means of tailoring the nickelhydroxide to a particular end use regardless of the contaminants presentin the secondary nickel.

For instance, a raw material blending step may include mixing asecondary nickel with a primary or other high purity nickel, such asanother secondary nickel. Nickel provided from secondary nickel andblended with a nickel of a higher purity provides a nickel source ofintermediate purity having a composition different from the initialsecondary nickel. Raw material blending may include either wet blending,dry blending or both. Dry blending may be accomplished by combiningmetal powder of a first secondary nickel source having a first puritywith a second nickel source having a second purity. Alternatively, wetblending may be used to produce a nickel starter material. Wet blendingmay be accomplished by combining a secondary nickel solution having afirst purity with a nickel solution having a second purity to provide anickel solution having a graded purity. For example, secondary nickelmay be provided in the form of a nickel sulfate solution. The secondarynickel sulfate solution may be mixed with a nickel sulfate solution ofhigher purity to reduce the concentration of contaminants in the totalnickel solution to a level suitable for use in making an active positiveelectrode material.

Also, the present method for making may include an intermediate blendingstep. An intermediate blending step may be carried out on one or moreintermediate solutions or solids by mixing the solutions or solids withan intermediate solution of higher purity n a fashion similar to that ofraw material blending. Shown in FIG. 3, is an example of a nickelhydroxide material having a target metal composition ofNi₉₃Co₅Zn_(0.5)Mg_(0.5)Ca_(1.0) made with a 50/50 blend of primarynickel sulfate solution and secondary nickel sulfate solution. Thus,while raw material blending is used to reduce contamination levels foran initial nickel source, an intermediate blending step may be used toreduce contamination of nickel sulfate just prior to feeding the MeSO₄into the nickel hydroxide production process.

The present method for making may also include a final product-blendingstep. A final product blending provides an enhanced nickel hydroxidematerial suitable for use in an electrochemical cell. The step for finalproduct blending is preferably a dry blending process, wherein a firstnickel hydroxide powder, produced in accordance with the method of thepresent invention and having a first purity is combined with one or morepowders of nickel hydroxide material having a composition which differsfrom the first nickel hydroxide. Preferably, the overall composition ofthe nickel hydroxide powder formed has a concentration of contaminantslower than that of the nickel hydroxide material formed without theblending step. Final product blending may therefore provide active,positive electrode material having significantly enhanced surface area,tap density, and crystallinity over that of a non-blended active,positive electrode material.

Nickel hydroxide materials having the target composition of(Ni₉₁Co_(4.5)Zn_(4.5))(OH)₂ were produced in accordance with the presentinvention using a single reactor system described above where one samplewas made with primary nickel sulfate and the other was made with asecondary nickel sulfate raw material blend. The nickel hydroxide madewith raw material blend used a 50/50 secondary nickel sulfate/primarynickel sulfate mixture to make nickel hydroxide. The active materialsproduced by each of the processes were formed into sealed c-cells in amanner well known in the art. Each c-cell was tested for capacity at ac/5 discharge rate at room temperature to compare blended final productwith non-blended nickel hydroxide. The results are listed below in Table2.

TABLE 2 COMPARISON OF NONBLENDED & BLENDED MATERIAL Primary NickelBlended Secondary Nickel Rate c/5 c/5 CAP (0.9 V)/Ah 4.65 4.61 % C/5 CAP100 100 CAP (1.0 V)/Ah 4.58 4.53 % C/5 CAP 98 97 MIDPOINT/V 1.24 1.24

The results in Table 2 show that nickel hydroxide material made withblended secondary nickel, does not suffer significant reduced capacityat a c/5 discharge rate.

Conventional preparation of nickel hydroxide materials using a secondarynickel source was not considered feasible until now, due to effects thatcontaminants may have on positive, battery electrode performance and theactive, positive electrode material. In fact, making nickel hydroxidematerial with a secondary nickel source using conventional methodsnormally fails to provide a nickel hydroxide material suitable for usein a battery electrode.

EXAMPLE

Four samples of a nickel hydroxide material were prepared from asecondary nickel source. Sample 1 was prepared using a simultaneousmixing/precipitation reaction as described in the specification above.Sample 2 was prepared using the same method as Sample I with an addedcarbonate precipitation step. Samples 3-4 were prepared in accordancewith the above-described method including the carbonate precipitationstep of Sample 2 with the additional evaporation/precipitation step asdescribed in the specification above. A summary of the results obtainedfor Samples 2, 3 & 4 are listed in Table 3.

Sample 1.

A secondary nickel sulfate solution containing high calcium (2 g/l) andsodium levels (15 g/l) was used to make nickel hydroxide material(Sample 1). The nickel hydroxide material was prepared using aprecipitation reaction. The Nickel hydroxide prepared with a secondarynickel sulfate solution with high sodium and high calcium was found tobe substandard with a low tap density (<2 g/cc). BET surface area wasfound to be high (>30 m /g) on these powders. Nickel hydroxide preparedusing this particular nickel sulfate solution was not suitable forbattery applications.

Sample 2.

A secondary nickel sulfate solution containing high calcium and sodiumlevels was used to produce a nickel hydroxide material (Sample 2) usingthe same method as in Sample 1 above, but further including a carbonateprecipitation reaction, water rinse, followed by conversion to nickelsulfate solution as described in the specification above. Afterconverting to nickel sulfate, the calcium concentration in the finalnickel solution was found to be about 0.4 g/l. Sodium, however, wasstill high at 14 g/l. Nickel hydroxide prepared using this secondarynickel sulfate solution yielded a powder having low tap densities(1.24g/cc) and high surface area (>30 m²/g). Such a powder was notsuitable for battery applications.

Samples 3-4.

A secondary nickel sulfate solution containing high calcium and sodiumlevels was used to produce nickel hydroxide material (Samples 3-4) usingthe same method as for Sample 2 but further including thecondensation/precipitation step as described in the specification above.In this case, after the nickel carbonate was converted to nickelsulfate, the nickel sulfate crystals were separated from the solutionand redissolved in water to form a nickel sulfate solution. Calcium andsodium levels in the nickel sulfate starter solution were found to be0.4 g/l, 3.9 g/l and 0.0, 2.2 g/l respectively for Samples 3 & 4. Nickelhydroxide powders were prepared from each nickel sulfate startersolution. Samples 3 & 4 showed suitable tap densities (˜2 g/cc) andsurface areas (˜25 m ²/g) for use as a positive electrode material in abattery.

TABLE 3 Composition Of Nickel Sulfate Element Sample 2 Sample 3 Sample 4Ni 139 g/l 130 g/l 137 g/l Co 0.0 0.0 0.0 Cd 0.0 0.0 0.0 Zn 0.0 0.0 0.0Fe 0.0 0.0 0.0 Cu 0.0 0.0 0.0 Mn 0.0 0.0 0.0 Pb 0.0 0.0 0.0 Ca 0.4 0.40.0 Mg 0.0 0.0 0.0 Na 14.0  3.9 2.2 Ni(OH)₂ Quality Poor Good Good

As the results in Table 3 demonstrate, the active material prepared witha secondary nickel without a carbonate addition and acondensation/precipitation step failed to produce a nickel hydroxidematerial suitable for use as a battery electrode material. The nickelhydroxide material produced with a secondary nickel in accordance withthe present method produces particles having a surface area, a tapdensity, and a crystallinity suitable for use as a battery electrodematerial.

While the invention has been illustrated in detail in the drawings andthe foregoing description, the same is to be considered as illustrativeand not restrictive in character. It is understood that only thepreferred embodiments have been shown and described fully and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed is:
 1. A method for making an active positive electrodematerial comprising the steps of: providing a secondary nickel sulfatesolution having a contamination that adversely effects the quality ofactive material for use as a battery electrode material; reducing thecontamination of the secondary nickel sulfate solution with at least oneprecipitation reaction to provide a treated secondary metal source; andconverting the treated secondary metal source into an active positiveelectrode material.
 2. The method of claim 1 wherein the step forreducing is a non-electrolytic process.
 3. The method of claim 1,wherein the at least one precipitation reaction includes a condensationprecipitation reaction.
 4. The process of claim 1, wherein the secondarynickel sulfate solution is an electroplating, electroless plating orelectrorefining process solution.
 5. The process of claim 4, wherein thesecondary nickel sulfate solution comprises at least 100 g/l of nickel.6. The process of claim 1, wherein the step for converting producesspherical nickel hydroxide particles.
 7. A method for making nickelhydroxide positive battery electrode material comprising the steps of:providing a secondary nickel salt solution having a contamination thatadversely effects the quality of nickel hydroxide material for use as abattery electrode material; reducing the contamination of the secondarynickel salt solution with at least one precipitation reaction to providea treated secondary nickel source; providing the treated secondarynickel source as a metal salt solution; and converting the metal saltsolution into an active positive battery electrode material.
 8. Themethod of claim 7, wherein the step for reducing is non-electrolytic. 9.The method of claim 7 wherein the precipitation reaction includes acondensation precipitation reaction.
 10. The method of claim 7, whereinthe secondary nickel salt solution is an electroplating, electrolessplating or electrorefining process solution.
 11. The method of claim 7,wherein the secondary nickel salt solution comprises at least 100 g/l ofnickel.
 12. The method of claim 7, wherein the step of converting themetal salt solution into an active positive battery electrode materialincludes a precipitation reaction.
 13. The method of claim 12, whereinthe precipitation reaction produces spherical nickel hydroxideparticles.
 14. The method of claim 7, wherein the precipitation reactionincludes at least one carbonate precipitation reaction.